16 – Desktop Fiber Laser: Colours Pt 4 The Rainbow’s End (50:12)

The Fiber Laser Learning Lab Series with Russ Sadler

In this Series, Lotus Laser have lent Russ a MOPA 20 watt fiber laser to “play with”. Although Russ has a moderate understanding of laser technology (his words) and how constant power glass tube systems work, pulsing desktop fiber laser marking machines are shrouded in a deeper mystery than the glass tube machines.

They have been designed for high speed marking and the technology has been well tried and proven. There are limited “tricks” that the pulsing laser technology can perform. You enter predefined parameters for each marking “trick” you wish the machine to deliver , then stand back in amazement. Most correspondents tell Russ that they have bought their machine direct from China and received a machine and EZCAD software, preloaded with a few default parameters. No other instructions beyond the EZCAD manual are forthcoming.

Russ states “I am neither a teacher or expert in this field so you join me in my learning adventure with the warning that I have a simple but inquisitive mind and will probably make mistakes on my way to discovering the truth. I WILL oversimplify and maybe distort the scientific detail in my quest to build a simple picture of why and how this technology works. I am not trying to reverse engineer anything, just to break through the seemingly impenetrable ‘techno cotton wool’ that surrounds this amazing piece of science.”


To be completed soon.

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Russ Sadler Next to the Desktop Fiber Laser
Russ Sadler Next to the Desktop Fiber Laser

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Transcript for Desktop Fiber Laser: Rainbow’s End

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0:00welcome to another fiber laser learning lab today’s session is entitled the end

0:05of the rainbow because I’m going to be quite brutal and we’re going to close

0:10the session on color marking stainless steel today now hope it’s going to be

0:16quite informative because I’ve been working labora Slee for the past few days putting hundreds of samples through

0:22this machine trying to zoom in on some colors that satisfy one of the grades

0:30that we talked about last time in my color grading system now later on we

0:35shall be looking at these colors under the microscope because it is very important to you understand where and

0:42how these colors come about and some of the I suspect untried new and tested

0:49methods that I have exploited to try and get these colors into a position where

0:55they are durable and fast to produce that most of the colors that you have

1:02seen to date mainly in the D category of my listing now I’ve got a few of those

1:08here and what I’m going to do initially is to just show you the difference

1:14between a B C and D great colors now we’re very fortunate today that despite

1:20it being a cold day um it’s a lovely sunny day outside and we should be able

1:27to step out into the sunshine and look at the durability of these colors in natural bright sunlight I’ve also got

1:36beside me here some LED white lights

1:42although I could use fluorescent as well I think these three main variations of

1:48light will demonstrate the point that I’m going to make I hope you can forgive the lawnmower in the background my name

1:53is busy cutting his grass very fortunately I don’t have any grass because my dad was a bit of a

1:59philosopher and he told me when I was younger never have any more grass than your wife will mow now had a slight

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

2:06change of plan because I think it’s a benefit to pass on

2:12if possible some of the experience that I’ve gained over the past few days of

2:17playing with all these parameters it’s given me a tremendous insight into just

2:22the huge variety of opportunities you’ve got on this machine for controlling the

2:28power down onto the surface of the material colors is all about heat per

2:34unit area and you can change the heat per unit area in so many different ways

2:41with this machine anybody getting one of these machines for the first time it’s likely to be extremely confused by all these

2:48parameters much the same as I was with practice I’ve managed to begin to

2:53understand the relative importance of some of these factors now this is a Mopa

2:59laser machine now one of the most confusing things about this machine is

3:05all the pulse types we’ve got pulses that are 2 nanoseconds long and we’ve

3:12got pulses that are 350 nanoseconds long now you achieve these pulses by running

3:18the machine at these specific frequencies now 850 killer answers let’s

3:24just call that a thousand a thousand kilohertz is a million cycles a second

3:29so that means every cycle equals one

3:34microsecond now over here we’ve got 350 nanosecond pulse but you achieve that at

3:4125 kilohertz and that means a frequency of 40 microseconds so it’s 40 times

3:49slower than this but the pulse is 350

3:55nanoseconds this pulse is 2 nanoseconds so in terms of pulse duration this one

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

4:04is effectively about 170 times longer than that one so this pulse here is a

4:11hundred and seventy times roughly a hundred and seventy times more than that one in terms of duration but it’s

4:19repetition rate the number of times that that pulse gets put down there’s 40 times slower and this is the strange

4:27balancing act what I’m first going to do is just quickly show you in a in a

4:32sample patch the difference between these two so you just get a feeling for

4:39the damage that these two extremes can do to the material and there we go that

4:49was a two nanosecond pulse did it do much damage so yes it did a little bit

4:57of damage to the surface as you can see but I’m going to use this as a classic example of something else that I’m going

5:03to talk about in a minute which is the light sensitivity of the patent that

5:08we’ve produced now I’m going to rotate this very slightly backwards and forwards and as I rotate it backwards it

5:18turns to black and as I rotate it forward I get the pattern back again and then it

5:26turns to black it’s got a very narrow viewing angle and that narrow that viewing angle that’s less than plus or

5:32minus ten degrees so I’m now going to go to the other extreme and I’m going to put a 350 no no second pulse in and

5:39we’ll do exactly the same test that all I’m going to change is spot size I think

5:46you can see the difference in the power there you can hear it and you can see it that is a pretty powerful pulse I’m

5:52using a hundred percent power I’m using two thousand millimeters a second for doing all this work and we’ve also got a

6:00line spacing of a hundred microns there’s that first one if we hold it in

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

6:06to the light just right we can see that there’s not a lot of difference in the color they’re both silvery white and if

6:12I start rotating them look the first one disappears and goes to black and the

6:19next one well that can go a long way look and it

6:25still remains white

6:33so one of the main advantages of this longer pulses we get a more durable mark

6:38on the surface we’re not just tickling the surface we’re damaging the surface there is a lot more complexity in these

6:44numbers to be to be analyzed when we get on to another section but I just wanted

6:51to show you the difference between these two palp pulse what types to start with now percent power is quite a complex

6:57factor it’s not as it’s not just a simple a matter of saying well when I

7:02get hundred percent power I should get X amount and when I put fifty percent power down I’m going to get 50 percent

7:09of the effect it’s not that simple I’m afraid so something we talked about

7:14quite a lot when we spoke about focus was the shape of the energy the

7:21intensity of the light within the laser beam the beam goes down to a focus point like

7:26this and at this point out here up for the focus we’ve got a certain amount of

7:33power let’s call it twenty watts it doesn’t really matter but there’s a fixed amount of power taking place there and that power is spread in a Gaussian

7:41fashion across the laser beam and let’s say it looks like this well if we squash the beam down to a

7:48smaller dimension we’ve got the same amount of power under the beam and

7:53effectively what it does it causes the laser beam profile to do this it squashes it

8:01up now I’ve drawn it upwards because that’s the way you normally see a graph but in reality we also got to be looking

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

8:07at it this way around and saying well I have been profile looks like that the intensity of this light is not

8:13uniform across the beam and as we move further and further away from the focal

8:19point although you would normally expect the beam to get weaker in fact it

8:24doesn’t get weaker at all depending on the amount of power that you put into the laser beam you could have this power 10 15

8:33millimetres below the focal point that you could do damage with that is

8:39effectively what a hundred percent power look like it’s a sharp pencil that’s the best

8:45way that I can describe it to you it’s like writing with a very sharp pencil when you reduce the power to 20% you’re

8:53doing effectively the same as this so you’re making it very much a smoother distribution at the focal point I know

9:01it’s a silly analogy but it’s probably something that will stick in your mind we’ve got a sharp pencil at 100% and a

9:07blunt pencil at 20% so there are many different ways of reducing the power into the surface but one of them is

9:14probably not percent power if you want a sharp crisp image if you want a soft

9:20gentle application of heat then you reduce the percent power let me try and

9:26prove that to you did you see it that was what 20% power

9:31was if you look extremely hard with a

9:36little bit of imagination you might be able to just see something there it is look we catch it in the light just right

9:43and we can see some surface marking so what we just seen there are two effects

9:49not only have we got a long pulse which is effectively a soft blunt pulse

9:55I would like to imagine it as because it’s not a sharp crisp pulse like this one so we just blunted this blood pulse

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

10:05with a blunt pencil and that means we’re not putting very much power down onto the surface at all we’re not damaging

10:11the surface very much at all now my analogies are very crude but there are

10:17images that I’m carrying in my mind and have helped me to understand the relationship between these very complex

10:23factors okay so we’ve got our blunt and sharp pencil analog for power so my

10:30images for these this range of pulses it runs from delicate and sharp to if you

10:37like brutal and blunt that is like a scalpel and that is like a lumberjack’s

10:43axe you wouldn’t perform brain surgery with that but you might perform brain surgery with that it’s a scalpel and an axe as

10:51we said now there is a serious interplay between these numbers here the frequency at

10:58which the the repetition frequency in which at which these pulses occur and the linear speed now before we jump on

11:06to speed which has a direct relationship to this there’s something else you need

11:13to understand about these shapes and I’m going to use this one as a good example

11:18as we said this is roughly one

11:25microsecond okay a millionth of a second

11:32but this pulse is only two nano seconds long and nanosecond is one thousandth of

11:39this division so just here where my line is is that pulse and we travel for a

11:49whole microsecond a millionth of a second before we get another pulse and

11:55then another millionth of a second before we get the next pulse so there is

12:02a huge space relative to the pulse size in between the pulses to the next pulse

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

12:09so if you like that is Heat then that is

12:16cooling so we put a little teeny-weeny spike of

12:22heat in and we have a huge amount of time over which it gets a chance to cool

12:28how on earth are we ever going to get any heat into this product well the answer is really because of the thermal

12:36reactivity of the material itself the material cannot cool this quickly it can

12:42heat up and eventually if you heat it enough times in the same spot it will

12:47get hotter and hotter and hotter because it does not get a chance to call in between the poses now that’s an

12:53important fact to remember that if we can put more heat into the same spot we

13:01will gradually raise the temperature of that spot now we come back to speed so

13:08when we look at my chart of the various frequencies and pulse lengths you’ll find that across the bottom here we’ve

13:14got a ratio which is 588 500 500 435

13:20they’re all in the 4 to 600 to 1 ratio okay so we’ve got a very long cooling

13:28period for a very short heating period regardless of the pulse so with our two

13:33nanosecond pulse at 2000 millimeters a second even though we’re running at 850

13:42kilohertz which is nearly a million times a second we’re only putting down

13:47425 pulses per millimeter if we reduce

13:52the speed to a thousand millimeters a second we double it 850 which means

13:59we’re putting twice as much power into the same millimetre of stroke so the

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

14:06slower the speed the more pulses we can get I mean down at 100 millimeters a

14:11second but getting half thousand pulses per millimeter if we were to drop it

14:16down to one millimeter a second we’d have nearly a million pulses we’d have

14:22850,000 pulses per millimeter there is a very interesting relationship there in an important relationship between speed

14:30and this frequency and that’s what this table attempts to show so we can

14:40effectively increase the power and the effectiveness of this pulse by

14:45decreasing the speed at which we apply them because as we slow the speed we get

14:52more pulses per millimeter and that means we’re going to do more damage by

14:58running slower here’s the first one that you can’t see which is two thousand

15:03millimeters a second with a two nanosecond pulse okay so now we’ve reduced the speed to 500 so it’s a

15:11quarter of what it was before at two thousand you can actually see the scan

15:18speed this time now two things I hope you’ll notice first of all we’ve got some color in there now look this one is

15:28a quarter of the speed of that one so there it was silver and now you’re getting a hint of color in it because

15:35what we’ve done we’ve increased the power and we’re actually burning effectively the metal we’re producing a

15:41yellow oxide film on the surface in terms of light sensitivity about the

15:52same look they’re just about responding the same and then if I tip it the other way from the light now they’re both disappearing at about

15:59at the same time and here’s my chart for the 350 nanosecond pulse we’re only

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

16:04running at 25 kilohertz remember so therefore the repetition rate is very very slow so we’re only getting 13

16:12pulses per millimeter at 2000 but look

16:18we did this amount of damage with just 13 pulses per millimeter if I reduce it

16:24to 500 I’m now going to put 50 pulses per milliliter in so I don’t think it

16:30takes a genius to realize that we’re going to put a lot more power into the surface and we’re going to do a lot more damage you should both see it and here

16:41now we’ve turned it into a very dark gold because we’ve put huge amount more heat into the surface what have we done

16:48to the light durability it was pretty good before

16:57that’s extremely durable as far as angle of light is concerned as I said this has

17:04been a fascinating insight into learning about the machine hunting for these colors and understanding the way in

17:11which the parameters work so we’ve seen the way that speed linear speed can

17:18affect the amount of power that we put down in the horizontal direction if we

17:23want to change the power in the vertical direction we have the opportunity to do that as well if we’re doing engraving

17:31which we are most of the time because this is a scanning engraving machine then what we have the opportunity to do

17:37is to play with the line spacing this way the pitch between lines now at the moment on this test patch I’m using a

17:46hundred microns spacing I’ve got a 60 micron beam on here and so effectively

17:52there’s dead space between the lines that you’re looking at on this pattern here you can’t see that because your eye

17:59is just not capable of looking at that resolution we shall see under the microscope but not with your eye let’s

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

18:06forget that mistake that I made there in this horizontal direction with that one we increase the power to the surface by

18:12approximately a factor of four in the horizontal direction so what I’m now going to do is I’m going to modify this

18:18one by changing the line spacing from a hundred microns to 25 microns which

18:24again has a ratio of about four to one so we should find that we come out with

18:30more or less the same color as this one because we’ve got the same amount of power going down per square millimeter

18:42so I think that demonstrates to you clearly that changing the power ratio in

18:47one direction is not exactly the same as changing the power ratio in the other direction there are differences we get

18:55more effective heat change by horizontal change than we do by vertical change and

19:03that’s an important lesson that I learned when I was hunting for these colors so these very coarse glittery

19:10colors as you can see are much more resistant to light change now the final

19:17factor which sometimes has very little effect it’s the hatch pattern so these are the

19:25important factors just here we’ve got this little pattern we’ve got the opportunity to change this type of

19:31hatching let’s just go from the standard lines are the fly back and the blue

19:37lines are the actual cut so in this particular instance we’ve got a cut which is always in that direction

19:44okay it’s called a uni directional cut

19:50we have the opportunity here of a bi-directional cut you’ll see there’s got red lines at the end which means

19:56that we’re not cutting and so we’re cutting in that direction and that direction that’s bi-directional scanning then

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

20:04we’ve got this really strange pattern here which I don’t know what the value of it is but hey it’s it’s there if you

20:11need it I’ve found it’s of no value to you for producing colors because you get tremendous change in the energy density

20:18as you work towards the center of the pattern the heating effect these are things you’ll have to find out for yourself but the critical one which is

20:26very useful once you’ve got one of these patterns selected then let’s choose that one which is the bi-directional scanning

20:32which is slightly faster than the unidirectional scanning but it’s it’s negligible as this thing here if we tick

20:41this box here crosshatch what that will do that will do a series

20:48of lines like that and then it will do a series of lines like that and that’s a

20:53very useful pattern which I’ve discovered for producing couple now in the last session I spoke about my color

20:59grading scheme which I was going to use to judge the success or failure of each

21:05one of the patches that I was making and I’ve refined it quite a lot since the

21:12last session and so what I’m saying here now is my a grade I need a very wide

21:18viewing angle greater than plus or minus 60 degrees and that’s with all light

21:25sources now today we’re likely to be checking it with a halogen light an LED

21:31light and daylight so that’s a pretty reasonable mix I have got florescent

21:37light in here but fluorescents are so many different colors that you know we’re gonna discount those at the moment

21:43when we just go with the three main sources of light that you’re likely to find these being exposed to now color

21:49fidelity is whether the color remains the same for all light sources for

21:56instance LED light has got a very narrow spectral range whereas daylight is wide

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

22:04and halogen light is a close approximation to daylight so we’re

22:09likely to see significant color change with LED lights a very important factor

22:17for me really decides whether these colors are good or bad is whether they can be put down quickly I mean this is

22:24not untypical of the sort of size image that you might want to work on I had to

22:31give up on this Moe village after about half an hour because that’s as far as it got we’re here the gold and the white or

22:38latte color we’ve got one minute twenty five and one minute forty eight they’re

22:43completely acceptable production times for an object that size all my little test squares have been rationalized to

22:51one square centimeter now regardless of whether that’s got any

22:57engraving in it or not one square centimeter is one square centimeter if

23:04you want to work out how long it’s going to take for this image to do you’re just going to have to put a little average

23:10rectangle around it and work out how many square centimeters are in there so this image for example is on average

23:16let’s just have a quick assessment a little bit dealing a little bit out so that’s roughly 6 centimeters 6

23:23centimeters by about 5 6 is a 30 square centimeters so if it takes five seconds

23:30per square centimeter and we’ve got 30 of them that’s going to take about just over two minutes so that’s just one

23:38color I’ve now got to add the area for each one of these other colors that I

23:43choose to put in here as well so but the time I’ve filled in all these here that

23:48could take five or six minutes to do is that acceptable could I charge out at a rate which would allow me to get a good

23:55recovery on this machine that’s a decision that you will have to take but it all depends on the speed of which you

24:01can put the colors down that’s production izing these colors so that they become useful so the factors for

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

24:07the other grades are similar but for instance a B grade instead of plus or

24:12minus 60 degrees I’ve nominally chosen plus or minus 30 degrees based on my experience it’s very likely that they

24:21could be as much as plus or minus 60 degrees they could be a grade viewing but they could be incredibly long as far

24:29as production time is concerned which throws them out of the a grade and puts

24:34them into a B grade where you may want to use them it’s up to your judgment as to whether or not it’s cost-effective C

24:40grade and degrade very similar except that C grade have got a little bit more

24:48viewing capability than a D grade which is very limited at about plus or minus ten degrees and to be honest most of the

24:56colors that you’re going to encounter from other manufacturers who tagged the

25:03color chart as you know the best thing since sliced bread hmm it’s not that good because you know

25:11I wouldn’t buy a machine based on something that I would classes degrade colors I’ll know user for examples to

25:18look at these various grading it’s gold on the end has turned orange the kingfishers blues in the middle are more

25:25green that mode is not bad so that’s holding its color but it goes

25:32look I only got to turn it by a very small amount of angle and it all changes

25:37now that’s quite nice orange on the end isn’t it I thought that was a gold but here in

25:44sunlight is definitely orange very

25:49quickly you can see how easily they’re all black now almost except with the

25:55gold one now let’s just rotate them around very very gently look at the color coming in and then all the color

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

26:04disappearing that’s why I call those rubbish I mean there’s a big great

26:10colors and let’s rotate the round and it’s quite a few of those that you see

26:16are pretty robust there are no way rotated

26:32and these are got quite a quite a wide viewing angle

26:40so we take a look at these in white light LED light we can see the chameleon

26:50color on the end there which is a mocha Gold come they’re moderately robust

26:59those colors but the problem is time in

27:06white light I mean these colors don’t look very much different than what they do in daylight

27:21sadly that’s it that check color palette very very limited Browns Silver’s golds

27:31or black pink in a move so don’t get

27:36excited to convert my conclusions about colors on stainless steel at least I’m

27:44going to run this little program in real time for you so settle down with a cup of coffee and off we go


















Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

32:11cool okay so that took about four and a half minutes and you can see my colors

32:21are pretty good they um they don’t change I move it around and this is in

32:29white light let’s go and have a look at in daylight so if it gets some Sun onto

32:35it then go we’re now in Nice sunlight

32:52well since I selected my color palette originally my a grade color palette I’ve been a bit more brutal with it and

32:59I’ve reduced it down to probably only about eight or ten drab colors well I

33:05say drab you’ve got some golds I’ve got some coppers some gray come green yeah I

33:13mean there’s a reasonable range there but it’s nothing like what you’re being

33:19sold and as you saw when this was being produced silver that silver around the

33:25outside that whitey silver is a nice rapid color to produce and you could use

33:31that on stainless steel it shows up very well as you can see but and gold as well

33:37also shows up well but apart from those two main colors I can’t see that you

33:43need many more for engraving texts on something but we’re gonna start looking

33:49at the degrade colors now this is I think without any surprise a gold that’s

33:5750 times magnification this is 400 times no surprises there hints of green but

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

34:05mainly yellows and rates net result you

34:11get what you see on the screen there’s no variation in depth so let’s take a look at the next one a bit of a sky blue

34:17game as I fiddle with the focus the color is just in the film itself in the

34:23oxide film on the surface next one is Kingfisher blue slightly different patination no they’re all everything’s

34:30at one depth there you just fiddle with the focus but nothing changes focus as I

34:35go up and down by one or two microns even now this came out as a salmon pink and sure enough I think you get what you

34:43see on the screen it’s a mixture of yellows and pinks but the predominant color when you look at it as salmon pink

34:50I think with more or less seen that pattern before in another bloom difficult to say where the focus is I

34:55think the focus is just about there so that’s the dark maroon color but

35:01again it’s flat run with the laser again twice and you get

35:08what you say which is blue okay so that’s a quick look at the C and D great

35:13colors which we’re not really interested in well I’m not interested in let me be fair about it what we’re gonna look at

35:21now is really my eighth-grade colors now the great thing about this color chase that I’ve been on is that they seem to

35:27be so much that people have not discovered about these colors or if they

35:33have discovered them they decide that they’re not worth pursuing or they’re rubbish the work that I’ve done has

35:39allowed me to discover three different basic types of color well I say types I

35:46mean textures you’ve now seen those that I disparagingly called D grades they are

35:52basically the principle of thin film interference which people have

35:58discovered to the eighth degree the colors that I’m interested in still using the thin film interference

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

36:03principle but looked a in a completely different way what you see on the screen

36:09there looks like I don’t know a piece of pink gravel well that’s exactly almost

36:16what it is it’s a disrupted surface which causes the light to change in so

36:23many different directions the thin film that’s on that surface cannot be pink

36:29there is no pink oxidation color so the only reason we’ve got pink is because

36:36there is already a mix of white light coming out to the to the microscope

36:43before it even reaches our eyes now look at the amount of black in there there is

36:49no indication of black when we look at that with the naked eye we only see a

36:55predominance of pink so that’s a gravel

37:00effect and we can look at that that’s looking at it at 50-times magnification if we just bump that up to 400 and take

37:08a look at it now I can’t get it in focus because there are so many there’s so much change of focal depth let’s come in

37:15and Ray is the table up so we picked the high spots up first in focus and here we go

37:23look we’ve got some high spots here coming into focus and then we’ll go up a

37:29little bit more and now we’ve got the stripes at the bottom of the valleys okay so that’s a three dimensional

37:37pattern you’ve got two forms of color mixing on that surface now the first form of light that you’re

37:42seeing there is from the tungsten lighting in the microscope you’ve got thin film interference off

37:49the surface which is creating the different colors yellows pinks and blues

37:54the flat surface at the bottom that lovely canary yellow that lovely pink

38:00they’re not in the color tempering range the only reason we can see them is

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

38:06because we’ve got an interference pattern which is affecting the light before even hits our eyes that’s what

38:13hits the microscope but the time it hits our eyes all those colors are Blumer

38:19ated and further interfered with and our eyes only see and the best I can show

38:25you is that that’s 50 times magnification by the time we see it’s 1 times magnification this surface is

38:32totally unpredictable in a strange sort of way it’s chaos here we’re getting

38:38variation in the thickness of the film superimposed on variation that we caused

38:43to the surface of the material so we’ve got ripples here like you see on the

38:48sand when that when the tide goes out that’s the second type of interference

38:55pattern that we’re perceiving with our eye there is a third one which I’m not sure that anybody has ever explored

39:01before and that’s something that I accidentally came across and revealed to

39:06you at the end of the last session now I’ve pursued this quite intensively

39:13because this is where the 8th grade colors really exist this as far as I’m

39:19aware is not something that people have ever been doing before to get color on

39:25stainless steel now he’s a gold where is the gold color coming from well

39:32it’s coming from the surface of the these little squares now this is not an

39:37area of science that I’ve seen anybody else working on discovering using

39:45exploiting what you’re seeing here is to the naked eye a lovely glittery gold

39:51what we’ve got here is a 60 micron laser beam and what we’ve got here is a 200 micron

40:00spacing and in between that grid we’ve created a heating effect on the surface

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

40:05now if you look at the color of each one of those squares you’ll see that what

40:10we’ve actually done we’ve created a flat thin film interference pattern on each

40:15one of those we’ve created a color which is pink yellowy

40:22whatever it is it hits the eye as a sparkly gold and it’s viewable from all

40:29sorts of directions and I think that’s purely because we’ve exploited the

40:35principle that we started off thinking about which is a cellular structure

40:41although they’re nano cell structures on a butterfly wing these are bigger but

40:48they’re exploiting the same effect we can go and look at that a little bit closer a lot closer at 400 Meg as I

40:55write use this image up and bring it into focus look at the black lines around the edge of the square that’s the debris on the side of the

41:01beam now carry on raising the focus up and you’ll see the surface come into

41:07focus and then I’ll raise it up more and

41:13you’ll see that the beam groove then coming into focus there so there’s a lot

41:18of depth in that picture now that’s not an incredibly powerful laser beam it’s one of

41:25the power beams it’s 100 burn a second pulse so it’s it’s in the fairly

41:31powerful region but it’s not certainly one of them powerful beams in fact I’ll tell you

41:36what let’s go and look at a powerful laser beam now this is silver 400 we’ve got

41:45two thousand millimeters a second speed and yet we’re only running at 25

41:51kilohertz frequency so what you’re able to see here is individual pulses and

42:03look at the metal that’s splashed up around each one of these pulses as soon

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

42:09as the liquid stainless steel hardens and it must have been liquid to produce these blobs we get a film an oxide film

42:20that is created on the surface as I mentioned to you probably in an earlier session from all the reading that I’ve

42:26done this oxide film forms within a few nanoseconds of the metal being exposed

42:33to oxygen so there will always be a film of some sort on the surface of stainless

42:38steel because of the interaction of chromium and oxygen and that effectively

42:44is freezing the color into the surface we’ve got the melted surface at the bottom of the laser beam and we’ve also got

42:52that surface there which is an undisturbed surface of the base material

42:57that has not been cut or melted and what you’re seeing there is the heating

43:04effect of the beam all around that little flat section it is caused its own

43:11thin film interference pattern of orange so there is a flat film interference

43:18pattern and the others are some three-dimensional pattern there is no green in the natural oxide colors so the

43:26only way that you can get green is by an interference pattern but of course those

43:32cauliflower shapes as I described them are not sticking up their little pits so

43:38you’ve got reflection off the inside of each one of those pits which is doing strange things to the interference

43:45patterns of light coming off surface and by the time it reaches your eye it looks like silver glittery silver

43:51now that I’m moving it to this sort of technology this is not predictable this

43:57is total chaos so there is little or no predictability to the color that I’m

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

44:04going to get it depends on the damage that I do to the surface and the heat that I put into the surface and the heat

44:10that I’m leaving behind in this residual undamaged area so let’s take a quick

44:16look at a few more of these colors so I will drop the magnification down to 200 so that we can see things quite quickly

44:22I’m just zooming in I’m just moving the focus around just so that you get an idea of the fact that there is quite a

44:28lot of variation in the depth of these things that’s a sort of a a latte color very light thorn it’s it’s mmm it’s on

44:37the edge of a bitter e gold but it’s it’s a little bit less than a gold now

44:43isn’t that beautiful now that’s a meet gold it’s quite a light a bright gold but you’ve got color

44:54in the beam as well there that’s an 8 known a second beam so in not doing as much damage with the beam itself and

45:01that’s why we can’t see the striations in the bottom of the laser beam because these are running at 250 kilohertz and we’re

45:09running the whole thing at 600 millimeters which is quite slow really relatively speaking but look here we’ve

45:16got enough heat to produce blue around the h of our square so that’s that’s one

45:24of the very fast Gold’s that I can produce takes about 2.9 or 3 seconds per

45:32square centimeter so this is exactly the same settings as the previous one except

45:37the speed has been changed from 600 to

45:43400 so in going down to 400 we’ve actually allowed more pulses per

45:49millimeter and we’ve had a greater heating effect so had gold has now

45:54changed into a copper color and maybe you could see that in the redness of the beam and that’s what’s

46:02probably causing the effect when it gets to the eye I hope to don’t me love this

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

46:09one this is like a almost a modern artwork this is actually a this actually comes

46:16out as a very very dark gold almost a brown now here’s another lovely silver

46:23and remember it’s not dissimilar to the silver that we first saw because this

46:30again looks like a field of collie flowers I mean this again is done with a

46:36maximum power laser beam 350 nano second beam but it’s running very slowly at 25

46:43kilohertz but we’re also running at quite high speed a thousand millimeters a second which is why you can see the

46:50spacing between the pulses so we’ve still got gold squares in there but we

46:56get no hint of gold when it meets our eye all we see is silver despite there being a lot of green in

47:03there and not much right now here we’ve got something that’s completely different to the eye this comes out as a

47:11smooth gold although this is very fast to produce at nine point five seconds it

47:18is not entirely durable as far as the viewing angle is concerned so I think I

47:26demoted this to a b-grade now you’ve seen this before because this

47:33is a silver in fact I have to say that to the eye this looks very white as

47:38opposed to silver should it does it look white not really so between physics and

47:47your brain there’s something weird going on okay any guesses as to what that

47:53might be in most likes this looks like a dark

48:01gray and it’s the dark gray that are used on the butterfly wing in other

Transcript for Desktop Fiber Laser: Rainbow’s End (Cont…)

48:08lights it’s got a little hint of brown in it this is definitely an iridescent color

48:14and yet can you see any hint of gray on that picture or any hint of brown as I

48:22said to you earlier this is chaos in action now most of the others as you

48:27have seen have been crosshatch pattern now this one isn’t a crosshatch pattern and it produces a matte finish any guess

48:37as to what the color might be jet black

48:44no it’s not dark gold that again is

48:51something you see on the butterfly wing so that’s enough of colors I think I’ve

48:57done enough research I think I’ve done enough discovery to set you guys on a

49:03trail if you wish to follow any of these directions and look for colors for

49:09yourself there are some new avenues here which I’m fairly confident have not been

49:14discovered before now the other interesting thought is for those guys

49:20with a q-switched laser looking at the very high powers and slow speeds and

49:27relatively low frequencies of some of these settings it is very possible that

49:33you might be able to use this technique to find colors on a q-switched laser I haven’t got a q-switched laser so I

49:40can’t experiment with it so I’m gonna leave this problem with you now I am NOT

49:47the user of this machine bear in mind I only play with this machine I get

49:53tremendous enjoyment from this machine and what you do with it is up to you

49:58so I think that’s a very convenient place to stop at this moment in time and say thank you very much for your

50:03patience and I’ll catch up with you in the next session where we will I promise not be

50:09touching colors

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Last updated April 25, 2024


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